Brazing is one of many ways frequently used to bond metal objects together. According to this bonding method, brazing metal is placed at the connection point between the two objects and they are heated until the brazing powder melts which in turn metallurgically bonds the objects together. Particularly in the aerospace industry, this is used to assemble various pans of a jet engine. For example, the rotors in the jet engine are formed from individual vanes which extend between inner and outer bands. These vanes are brazed to the inner and outer bands. Also, around the engine housing is a honeycomb material which acts as an abradable seal between the housing and the rotor assembly. This honeycomb must also be brazed or bonded to an engine part or assembly. Combustion liners are also formed by brazing metal sheets together.
Using brazing powders is particularly difficult and inefficient. Getting the brazing powder in position, in the fight quantities evenly distributed is difficult. Maintaining it in position is also difficult.
There are composite products which are the braze powders held together by binding material. But the product is relatively rigid and requires special forming tools that are very expensive with thinner small cell honeycomb material. Due to the nature of the product, it is very difficult to use. Other binders are unsuitable because they leave ash behind on the surface which interferes with the bonding or corrode the treated metal surface.
Other products and brazing atmospheres may cause an oxide to form on the metal surface. The oxide interferes with the formation of a good bond. The oxides are a problem with alloys of aluminum, timium, hafnium and chromium. To avoid this, the products are nickel coated prior to brazing to avoid oxide formation. This is obviously very expensive. It also may require the pan being nickel coated to be partially masked to avoid nickel coating undesired portion of the article.